Various industrial processes employ reciprocating machinery having a linear stroke to implement the process. In die casting and plastic molding, for example, the linear reciprocating device is an hydraulic cylinder used for loading raw material into the die or mold respectively. In die casting, molten metal is forced into the die from the hydraulic cyliner by a piston type plunger or ram displaced over a linear stroke under controlled operating conditions of pressure and velocity. Research in die casting has achieved a level of sophistication whereby the proper injection speeds, pressure and temperatures required for optimum operation for any given machine can be theoretically calculated. To satisfy the calculated conditions, the operation must be carried out within narrow ranges of settings for each of the critical process parameters. Variation in one or more of the process parameters will affect the performance of the other parameters on the process and will alter the production rate and affect the yield of the product produced. To optimize the production output the process parameter settings are adjusted over a series of production runs until a product with desired characteristics and production yield is obtained. Since the events which affect the production cycle occur much too quickly for human observation it was necessary, heretofore, for operating personnel to make subjective judgements in adjusting process parameters in a production run frequently resulting in high scrap rates. The trial and error technique commonly used heretofore also required more raw material than necessary in getting a given required production output. Moreover, because of the inability to control and adjust the process parameters accurately, the design of the article produced typically had to be made with more material than necessary for functional or strength considerations simply to permit an acceptable yield.
Accordingly, a need exists for a diagnostic instrumentation system which can readily be applied to the process machinery to monitor and record objective measurements of machine performance during an actual production cycle. The objective measurements should represent machine operational data which will provide technical personnel with the means to make appropriate adjustments to maintain optimum process integrity. Prior art instrumentation claiming to satisfy this need are based upon the use of high speed analog graphic plotters which typically use expensive ultraviolet sensitive photographic paper in combination with transducers and signal conditions designed to collect machine data and display it. One of the major disadvantages to the use of a graphic plotter is that its output is a graphical display of the given parameter under observation versus time. A time display is difficult to interpret and requires sophisticated expertise to derive and calculate quantitative values for the critical parameters affecting the process. Not only is the interpretation subject to error but it does not provide readily apparent information from which machine adjustments may be made in the next production cycle. Another significant disadvantage is that the oscillographs must be adjusted to accommodate the transducers used on a specific machine and must be calibrated for each different type of transducer. Also, because of the high speed of the paper travel of the recorder it is necessary for a technical person to be constantly attentive of the oscillograph so as to minimize the waste of the expensive paper.
In a die casting operation the reciprocating device would be representative of the hydraulic cylinder and piston ram for injecting raw material into the die. In accordance with the method of the present invention a profile of the critical operational parameters of the reciprocating device, viz., velocity and pressure, are generated as a function of ram position along its linear stroke. This permits dramatically reduced set up time and readily provides information for adjustment of the variable parameters within precise limits to assure maximum production quality and performance.